The present invention relates to an x-ray analysis application. More specifically, the present invention relates to an apparatus and method for generating, forming, and directing an x-ray beam used in x-ray analysis.
A common method used to study moderately ordered structures, i.e. those structures which have short range ordering but lack long range ordering, is small angle x-ray scattering. The method is based on illuminating a sample structure with a beam of x-rays. A portion of the x-ray beam is not able to travel directly through the sample structure, rather some rays are deflected or scattered and emerge from the sample at varying angles. The incident x-rays make their way along the spaces between the atoms of the structure or are deflected by the atoms. Since the structure is ordered throughout with short range ordering, the scattering from the structure will create a diffused x-ray pattern at a very close range to the x-rays traveling directly through the structure. This diffused pattern corresponds to the atomic structural arrangement of the sample.
Small angle x-ray scattering can be done in one or two dimensions. One dimensional small angle x-ray scattering utilizes a line source to maximize x-ray flux. The resultant diffusion pattern formed by the line source reveals information in only one dimension. Two dimensional x-ray scattering utilizes an x-ray point source which makes it possible to reveal two dimensional information. Although a rotating anode is preferred as a laboratory x-ray point source, other x-ray generators, including sealed tubes, may be used. A synchrotron has also been used in two-dimensional applications due to its well-collimated and high intensity beam.
Traditionally, an x-ray beam used in two dimensional small angle scattering is formed by a series of slits or pinholes to collimate the divergent beam and limit scattering effects from the slits. For samples with strong scattering power or a large scattering angle, such as crystals, parasitic scattering from pinholes and mirrors can be ignored. A two pinhole system may be used in such an application. For samples with weak scattering power or a small scattering angle, such as those contemplated by the present invention, a three pinhole system is preferably used. The current techniques for small angle scattering involve the use of pinhole systems, filters, and total reflection mirrors. A Ni filter, graphite or other crystals are used in a pinhole system or a pinhole+total reflection mirror system to reduce the K.beta. radiation or other continuous spectrum radiation. Total reflection mirrors such as Kirkpatrick-Baez or cross-coupled mirrors are frequently used with the pinhole systems (both with two-pinhole systems and three pinhole systems). Presently, the focal point of a total reflection mirror used with a pinhole system is always set at the detector position, creating a loss of flux. Parabolic multilayer optics (Kirkpatrick-Baez, or cross-coupled) are also used in small angle scattering systems but fail to enhance the beam at the sample position effectively.
Small angle x-ray scattering systems presently used in the art suffer from noise problems caused by pinhole scattering and limited x-ray flux used for generating x-ray scattering patterns. Thus, there is a need in the art for a small angle x-ray scattering system which eliminates diffraction noise and increases the flux on a sample.